This invention relates to the coating or plating of substrates using glow discharge and thermal vaporization in a vacuum chamber.
In the past, various techniques have been used to deposit a film or coating on a substrate located in a vacuum chamber. One technique simply is to thermally vaporize or evaporate a metal, permitting the vapor to condense and be deposited on the substrate. Another method is referred to as chemical vapor deposition wherein different gases are introduced into the vacuum chamber to react and form a compound on the substrate. Yet another prior art method is referred to as sputtering. In this method, a vacuum or gas filled discharge tube has a cathode that is disintegrated by bombardment, so that the cathode material is vaporized and deposited on the substrate.
A variation of these methods is shown in U.S. Pat. No. 2,501,563 issued to W. H. Colbert. In this patent, vacuum evaporation is used to vaporize and deposit a metal substrate. Gas is then introduced into the vacuum chamber to oxidize the metal and form a metallic compound coating. Another variation of the prior art methods is shown in U.S. Pat. No. 3,318,790 issued to B. G. Carbajal III, et al. In this patent, a gaseous organic source material is introduced into a vacuum chamber and a glow discharge is established to polymerize the source material and deposit same on the substrate.
A difficulty with the prior art methods is that they generally do not permit individual and independent control of each parameter of the process and hence do not permit the fabrication of "tailor-made" compounds having predetermined atom ratios and hence predetermined properties.